Sensor Device

ABSTRACT

Provided is a sensor device that suppresses a malfunction caused by a negative surge or a voltage drop. A sensor device includes a sensor element having an electrical characteristic varying according to a physical amount, a signal processing circuit configured to process an output signal of the sensor element, a transistor element interposed between a power source terminal and the signal processing circuit, a resistive element configured to connect a drain and a gate of the transistor element, or a collector and a base of the transistor element, and an element having threshold voltage for connecting the gate or the base of the transistor element to a GND. The element regulates current flowing from the resistive element in a direction of the GND, in a case in which supply voltage to the signal processing circuit falls below the threshold voltage.

TECHNICAL FIELD

The present invention relates to a sensor device supplied with powerfrom the outside, and particularly to a sensor device having breakdownresistance and malfunction resistance to a negative surge that occurs ina power line.

BACKGROUND ART

If a negative surge or a voltage fluctuation occurs in a power line,supply voltage to a load circuit becomes negative voltage, and reversecurrent flows in the load circuit, so that breakdown may occur. As aconventional technique addressing such an issue, there is a techniquedescribed in PTL 1.

The technique described in PTL 1 is configured to divide supply voltageto a P-type FET provided between a power source and a load circuit, andto the load circuit, via a resistor, and to input intermediate voltagethereof to a gate of the P-type FET. The load circuit is protected inthe following manner. When an input-side polarity is normally connected,the P-type FET enters an ON state to supply source voltage to the loadcircuit, and when the input-side polarity is reversely connected, theP-type FET enters an OFF state so that reverse polarity voltage is notapplied to the load circuit.

CITATION LIST Patent Literature

PTL 1: JP-2000-341848-A

SUMMARY OF INVENTION Technical Problem

In recent years, however, there has been an increasing demand for costreduction, and it is necessary to simplify a protection circuit providedon the outside of a conductor chip. In this case, a negative surge or avoltage drop that continues for a relatively longer time than that inconventional circuits occurs in a power line. If load circuit sidevoltage falls below threshold voltage of the P-type FET, the P-type FETturns OFF. As a result, electrical charge accumulated in the loadcircuit stops being discharged to a power source side via the P-typeFET. Nevertheless, if the negative surge continues even after thisstate, electrical charge accumulated in the load circuit via voltagedivision resistors continues to be discharged. Finally, the accumulatedelectrical charge is fully discharged. In response to the fulldischarge, the load circuit is reset. Thus, a malfunction such as anabnormal value output and a restarting operation may occur.

The present invention has been devised in view of the above-describedsituations, and the object of the present invention is to provide asensor device that has high malfunction resistance, and suppresses avoltage drop in a load circuit even if a negative surge or a voltagedrop that continues for a relatively long time occurs in a power line.

Solution to Problem

To achieve the above-described object, a sensor device according to thepresent invention includes a sensor element having an electricalcharacteristic varying according to a physical amount, a signalprocessing circuit configured to process an output signal of the sensorelement, a transistor element interposed between a power source terminaland the signal processing circuit, a resistive element configured toconnect a drain and a gate of the transistor element, or a collector anda base of the transistor element, and an element having thresholdvoltage for connecting the gate or the base of the transistor element toa GND. The element regulates current flowing from the resistive elementin a direction of the GND, in a case in which supply voltage to thesignal processing circuit falls below the threshold voltage.

Advantageous Effects of Invention

The present invention can provide a sensor device that has highmalfunction resistance, and can suppress a voltage drop in a loadcircuit even if a negative surge or a voltage drop that continues for arelatively long time occurs in a power line.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a configuration of a sensor device according to afirst embodiment.

FIG. 2 illustrates a configuration of a sensor device according to asecond embodiment.

FIG. 3 illustrates a configuration of a sensor device according to athird embodiment.

FIG. 4 illustrates a configuration of a sensor device according to afourth embodiment.

FIG. 5 illustrates a configuration of a sensor device according to afifth embodiment.

FIG. 6 illustrates an example of an internal power source voltagefluctuation waveform obtainable when a negative surge is applied,according to the technique of the present invention.

FIG. 7 illustrates an example of an internal power source voltagefluctuation waveform obtainable when a negative surge is applied,according to a conventional configuration.

FIG. 8 illustrates a configuration of a conventional sensor device.

FIG. 9 illustrates an application example of the sensor device accordingto the fifth embodiment.

FIG. 10 illustrates an application example of the sensor deviceaccording to the fifth embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described below withreference to the drawings.

A sensor device according to a first embodiment of the present inventionwill be described with reference to FIGS. 1, 6, 7, and 8. FIG. 1illustrates a configuration of the sensor device according to the firstembodiment. FIG. 6 illustrates an example of an internal power sourcevoltage fluctuation waveform obtainable when a negative surge isapplied, according to the technique of the present invention. FIG. 7illustrates an example of an internal power source voltage fluctuationwaveform obtainable when a negative surge is applied, according to aconventional configuration. FIG. 8 illustrates a configuration of aconventional sensor device.

The configuration of the sensor device according to the first embodimentwill be described with reference to FIG. 1.

A sensor device 1 according to the first embodiment includes a powersource terminal 2 for supplying voltage Vb, a GND terminal 3, a sensorelement 20 for generating an electric signal according to a physicalamount, and a sensor circuit 10 for supplying power to the sensorelement 20 and processing an output signal from the sensor element 20.The sensor circuit 10 includes a signal processing circuit 11 forprocessing an output signal from the sensor element 20, a P-typefield-effect transistor (hereinafter, referred to as “PMOS”) 12interposed between the power source terminal 2 and the signal processingcircuit 11, a resistor 14 for connecting a drain and a gate of the PMOS12, and a PMOS 13 for connecting the gate of the PMOS 12 to a GND. Agate and a drain of the PMOS 13 are connected to the GND, and a sourcethereof is connected to the gate of the PMOS 12. The PMOS 13 hasthreshold voltage Vth1, and when source voltage of the PMOS 13 is largerthan the threshold voltage Vth1, the PMOS 13 turns ON.

The function of the sensor device according to the first embodiment willbe described with reference to FIGS. 1 and 7.

In normal times, the source voltage of the PMOS 13 is larger than thethreshold voltage Vth1. Thus, the PMOS 13 turns ON, and current Is flowsfrom the drain of the PMOS 12 to the GND via the PMOS 13. When aresistance value of the resistor 14 is sufficiently larger than ONresistance of the PMOS 13, the PMOS 12 enters an ON state, so thatconduction is established between the power source terminal 2 and thesignal processing circuit 11. Then, supply voltage Vs is supplied fromthe power source terminal 2 to the processing circuit 11. The sensordevice 1 according to the first embodiment is configured to supplysource voltage to the signal processing circuit 11 via the PMOS 12 innormal times, and can supply the stable supply voltage Vs to theprocessing circuit 11 irrespective of temperature because the PMOS 12has a smaller voltage drop as compared with a parasitic diode.

On the other hand, if the supply voltage Vs abnormally drops due to anegative surge or the like, the PMOS 13 autonomously turns OFF at thetime when the source voltage of the PMOS 13 reaches the thresholdvoltage Vth1. Upon the PMOS 13 turning OFF, the current Is that has beenflowing in the PMOS 13 stops. Accordingly, the gate and the drain of thePMOS 12 have the same potential. Thus, even if the source voltage of thePMOS 12 fluctuates toward a negative side with respect to drain voltageof the PMOS 12, the PMOS 12 does not turn ON, and electrical chargeaccumulated in the signal processing circuit 11 is maintained. The PMOS13 autonomously turns OFF at the time when the source voltage of thePMOS 13 reaches the threshold voltage Vth1. It is therefore possible tosurely turn OFF the PMOS 12.

The PMOS 13 turns OFF at the time when the source voltage reaches thethreshold voltage Vth1. The PMOS 13 thereby regulates the flow of thecurrent Is. Thus, even if a negative surge or the like occurs andcontinues for a relatively long time, electrical charge accumulated inthe processing circuit via the resistor 14 can be prevented from beingfully discharged. The supply voltage Vs of the processing circuit 11 ismaintained in the vicinity of threshold voltage Vth. Thus, by settingthe threshold voltage Vth to a voltage value equal to or larger thanstored information of a memory provided in the processing circuit 11,the malfunction of the sensor device can be prevented.

In addition, for preventing the operation delays of the PMOS 12 and thePMOS 13, it is desirable to connect a well of the PMOS 12 and a well ofthe PMOS 13 to a node on the supply voltage Vs side to stabilize voltageof each well. Thus, the well of the PMOS 12 is connected to the drain,and the well of the PMOS 13 is connected to the source.

In contrast, the function of the sensor device according theconventional configuration will be described with reference to FIGS. 8and 9. According to the conventional configuration, if the sourcevoltage Vb falls below threshold voltage Vth2 of the PMOS 12, the PMOS12 turns OFF. At this time, the supply voltage Vs drops to about thethreshold voltage Vth2. Then, electrical charge accumulated in thesignal processing circuit 11 continues to be discharged via resistors 14a and 14 b. Finally, all the electrical charge is lost. Thus, the supplyvoltage Vs fails to be maintained, so that the malfunction of the sensordevice may be caused.

The effects of the sensor device according to the first embodiment willbe summarized.

The first effect lies in that the sensor device is configured to supplysource voltage to the signal processing circuit 11 via the PMOS 12 innormal times, and can supply the stable supply voltage Vs to theprocessing circuit 11 irrespective of temperature because the PMOS 12has a smaller voltage drop as compared with a parasitic diode.

The second effect lies in that the malfunction of the sensor can beprevented because the drop in the supply voltage Vs to the signalprocessing circuit 11 can be maintained in the vicinity of the thresholdvoltage Vth1 of the PMOS 13 even if a negative surge or a source voltagedrop that continues for a long time occurs.

The third effect lies in that the PMOS 12 can be surely turned OFFbecause the PMOS 13 autonomously turns OFF at the time when the sourcevoltage of the PMOS 13 falls below the threshold voltage Vth1.

A sensor device according to a second embodiment of the presentinvention will be described with reference to FIG. 2. FIG. 2 illustratesa configuration of the sensor device according to the second embodiment.In addition, the description of the points overlapped with the firstembodiment of the present invention will be omitted.

A sensor device 1 according to the second embodiment is characterized inthat a capacitor 16 is connected in series to the signal processingcircuit 11 in the sensor device 1 according to the first embodiment. Alow-pass filter including ON resistance of the PMOS 12 and the capacitor16 is thereby formed. This can make it difficult to transmit afluctuation in the source voltage Vb to the supply voltage Vs. Inaddition, the amount of electrical charge that can be accumulated isincreased by the capacitor 16. It is therefore possible to suppress thedrop amount of the supply voltage Vs with respect to a discharge amount.Thus, the second embodiment of the present invention can further improvenegative surge resistance.

A sensor device according to a third embodiment of the present inventionwill be described with reference to FIG. 3. FIG. 3 illustrates aconfiguration of the sensor device according to the third embodiment. Inaddition, the description of the points overlapped with the firstembodiment of the present invention will be omitted.

A sensor device 1 according to the third embodiment includes a PNPbipolar transistor (hereinafter, referred to as “PNP transistor”) 15 anda PNP transistor 17, instead of the PMOS 12 and the PMOS 13 in thesensor device 1 according to the first embodiment. An emitter of the PNPtransistor 15 and a power source terminal 2 are connected, a collectorof the PNP transistor 15 and a signal processing circuit 11 areconnected, and a base of the PNP transistor 15 and an emitter of the PNPtransistor 17 are connected. A collector and a base of the PNPtransistor 17 are connected to the GND. In normal times, base currentsIb1 and Ib2 flow in the PNP transistors 15 and 17. The PNP transistors15 and 17 accordingly enter the ON state. If the supply voltage Vs fallsbelow threshold voltage Vth of the PNP transistor 17, the PNP transistor17 enters an OFF state. At the same time, base voltage and collectorvoltage of the PNP transistor 15 have the same potential. Thus, even ifemitter voltage of the PNP transistor 15 fluctuates toward a negativeside with respect to collector voltage, the PNP transistor 15 does notturn ON, and electrical charge accumulated in the signal processingcircuit 11 is maintained. The supply voltage Vs can be accordinglymaintained in the vicinity of the threshold voltage Vth of the PNPtransistor 17. The sensor device according to the present embodiment canobtain the effects similar to those of the sensor device according tothe first embodiment. Furthermore, since bipolar transistors can flowlarger current than that in MOSFETs, bipolar transistors are suitablefor a sensor device with large power consumption.

A sensor device according to a fourth embodiment of the presentinvention will be described with reference to FIG. 4. FIG. 4 illustratesa configuration of the sensor device according to the fourth embodiment.In addition, the description of the points overlapped with the firstembodiment of the present invention will be omitted.

A sensor device 1 according to the fourth embodiment includes a PNjunction diode 18 instead of the PMOS 13 in the sensor device 1according to the first embodiment. A connection point between a resistor14 and a gate of a PMOS 12 is connected to an anode of the PN junctiondiode 18, and a cathode of the PN junction diode 18 is connected to theGND. In normal times, forward current Id flows in the PN junction diode18. The PMOS 12 accordingly turns ON. If supply voltage Vs falls belowforward voltage Vd of the PN junction diode 18, the forward current Idis regulated by the PN junction diode 18, so that a gate and a drain ofthe PMOS 12 have the same potential. Thus, even if the source voltage ofthe PMOS 12 fluctuates toward a negative side with respect to drainvoltage, the PMOS 12 does not turn ON, and electrical charge accumulatedin the signal processing circuit 11 is maintained. The supply voltage Vscan be accordingly maintained in the vicinity of the forward voltage Vdof the PN junction diode 18. The sensor device according to the presentembodiment can obtain the effects similar to those of the sensor deviceaccording to the first embodiment.

A sensor device according to a fifth embodiment of the present inventionwill be described with reference to FIG. 5. FIG. 5 illustrates aconfiguration of the sensor device according to the fifth embodiment. Inaddition, the description of the points overlapped with the firstembodiment of the present invention will be omitted.

A sensor device 1 according to the fifth embodiment includes a PNjunction diode 18 b connected in series to the PN junction diode 18 inthe sensor device 1 according to the fourth embodiment. With thisconfiguration, if supply voltage Vs drops to fall below a doubled valueof forward voltage Vd of the PN junction diodes 18 and 18 b, forwardcurrent Id is regulated, so that a gate and a drain of the PMOS 12 havethe same potential. Thus, even if the source voltage of the PMOS 12fluctuates toward a negative side with respect to drain voltage, thePMOS 12 does not turn ON, and electrical charge accumulated in thesignal processing circuit 11 is maintained. The supply voltage Vs can beaccordingly maintained in the vicinity of the doubled value of theforward voltage Vd of the PN junction diodes 18 and 18 b. The sensordevice according to the present embodiment can obtain the followingeffect in addition to the effects of the sensor device according to thefirst embodiment. More specifically, the effect lies in that holdvoltage of the supply voltage Vs can be adjusted according to the numberof series-connected PN junction diodes.

In addition, the above-described technique of adjusting hold voltage canbe realized by using a P-type field-effect transistor or a PNP bipolartransistor. For example, as illustrated in FIG. 9, there is a method offurther adding a PMOS 13 b between the GND and the drain of the PMOS 13of the sensor device 1 according to the first embodiment, connecting thegate and the drain of the PMOS 13 to a source of the PMOS 13 b, andconnecting a gate and a drain of the PMOS 13 b to the GND. In addition,as illustrated in FIG. 10, there is a method of further adding a PNPtransistor 17 b between the GND and the collector of the PNP transistor17 of the sensor device 1 according to the third embodiment, connectingthe base and the collector of the PNP transistor 17 to an emitter of thePNP transistor 17 b, and connecting a base and a collector of the PNPtransistor 17 b to the GND. Also in the case of using each of theabove-described configurations, hold voltage of the supply voltage Vscan be adjusted.

REFERENCE SIGNS LIST

1: sensor device, 2: power source terminal, 3: GND terminal, 10: sensorcircuit, 11: signal processing circuit, 12: MOSFET, 13: MOSFET, 14:resistor, 15: transistor, 16: capacitor, 17: transistor, 18: diode, 19:diode, 20: sensor element

1. A sensor device comprising: a sensor element having an electrical characteristic varying according to a physical amount; a signal processing circuit configured to process an output signal of the sensor element; a transistor element interposed between a power source terminal and the signal processing circuit; a resistive element configured to connect a drain and a gate of the transistor element, or a collector and a base of the transistor element; and an element having threshold voltage for connecting the gate or the base of the transistor element to a GND, wherein the element regulates current flowing from the resistive element in a direction of the GND, in a case in which supply voltage to the signal processing circuit falls below the threshold voltage.
 2. The sensor device according to claim 1, wherein the transistor element is a first field-effect transistor, and wherein a source of the first field-effect transistor and the power source terminal are connected, a drain of the first field-effect transistor and the signal processing circuit are connected, and a gate of the first field-effect transistor is connected to the GND via the element.
 3. The sensor device according to claim 2, wherein the element is a second field-effect transistor, and wherein a source of the second field-effect transistor and the gate of the first field-effect transistor are connected, and a drain and a gate of the second field-effect transistor and the GND are connected.
 4. The sensor device according to claim 3, wherein a well of the first field-effect transistor is connected to a drain of the first field-effect transistor, and a well of the second field-effect transistor is connected to the source of the second field-effect transistor.
 5. The sensor device according to claim 2, wherein the element is a transistor circuit including a plurality of series-connected field-effect transistors, and wherein a source of the transistor circuit and the gate of the first transistor are connected, and a drain and a gate of the transistor circuit and the GND are connected.
 6. The sensor device according to claim 2, wherein the element is a PN junction diode, and wherein an anode of the diode and the gate of the first field-effect transistor are connected, and a cathode of the diode and the GND are connected.
 7. The sensor device according to claim 2, wherein the element is a diode circuit including a plurality of series-connected PN junction diodes, and wherein an anode of the diode circuit and the gate of the first field-effect transistor are connected, and a cathode of the diode circuit and the GND are connected.
 8. The sensor device according to claim 1, wherein the transistor element is a first PNP transistor, and wherein an emitter of the first PNP transistor and the power source terminal are connected, a collector of the first PNP transistor and the signal processing circuit are connected, and a base of the first PNP transistor is connected to the GND via the element.
 9. The sensor device according to claim 8, wherein the element is a second PNP transistor, and wherein an emitter of the second PNP transistor and the base of the first PNP transistor are connected, and a collector and a base of the second PNP transistor are connected to the GND.
 10. The sensor device according to claim 8, wherein the element is a transistor circuit including a plurality of series-connected PNP transistors, and wherein an emitter of the transistor circuit and the base of the first PNP transistor are connected, and a collector and a base of the transistor circuit and the GND are connected.
 11. The sensor device according to claim 8, wherein the element is a PN junction diode, and wherein an anode of the diode and the base of the first PNP transistor are connected, and a cathode of the diode and the GND are connected.
 12. The sensor device according to claim 8, wherein the element is a diode circuit including a plurality of series-connected PN junction diodes, and wherein an anode of the diode circuit and the base of the first PNP transistor are connected, and a cathode of the diode circuit and the GND are connected.
 13. The sensor device according to claim 1, wherein the sensor device includes a capacitor series-connected to the signal processing circuit.
 14. The sensor device according to claim 1, wherein threshold voltage of the element is a voltage value equal to or larger than information stored in a memory of the processing circuit. 